Lack of blood flow (ischemia) to the eye may result in death of the tissues in the optic nerve and retina/choroid. In the case of central retinal artery occlusion (CRAO), there is a particle (embolus) in the major blood vessel giving oxygen and nutrients to the retina. In the case of anterior ischemic optic neuropathy (AION), there may be an occlusion of the blood vessel (s) entering the eye in the anterior optic nerve. With optic neuritis (ON) involving the anterior optic nerve, there is an inflammation of the optic nerve due to disease in the myelin sheath, the covering of the nerve fibers that exit the eye. After a period of time (minutes to hours to days), death of the tissue may occur causing irreversible damage.
Pathology to tissues of the eye may occur due to blunt injuries, such as a blow to the eye/orbit, resulting in hemorrhage within or around the eye and associated swelling of eye tissue. Unfortunately, it is often difficult to control injury to the eye using conventional ophthalmological means including medical and surgical intervention.
Various other diseases of the eye and the orbit may result in swelling of tissue with consequent loss of function. Inflammation of orbital tissue is usually managed with systemic medical therapy or even surgical decompression. Other types of inflammation of the tissues within the eye include posterior uveitis, choroiditis, retinitis, vitritis, scleritis, thyroid-related eye disease, phacoanaphylaxis, anterior uveitis, and sympathetic ophthalmia. Secondary glaucoma may result from inflammation involving the anterior segment of the eye.
Infections of the eye may involve the cornea, the sclera, the vitreous, the retina/choroid, the ciliary body, the lens, and the anterior chamber. They are usually treated with systemic antibiotics, sometimes systemic steroids, and topical drops of antibiotics, and intraocular antibiotic injections.
Current treatment for swelling or inflammation of the eye and orbit is not always satisfactory. In the severely injured eye or orbit, medical therapy to control swelling is usually applied systemically resulting in high levels of medication in the rest of the body with very low concentrations reaching the eye or orbit. Surgical intervention to decompress the eye and/or orbit requires major intervention through opening the bony walls of the orbit or skull to expose the area and prevent compression against the fixed volume of the bony walls. In the case of severe swelling of the sheath around the optic nerve, surgical decompression of the sheath has been attempted in severe cases of papilledema, anterior ischemic optic neuropathy, and severe trauma. The results have variable reports of success and failure of the procedures.
Hypothermia has proved encouraging in the recent literature for the purpose of decreasing oxygen consumption and for decreasing swelling of the brain and other central nervous system (CNS) tissue. Since the eye is part of the CNS, it seems logical that hypothermia of the eye may decrease swelling of the eye and optic nerve in the same way as hypothermia of the brain prevents brain swelling. Unfortunately, cooling of the entire body to cool the brain does have inherent dangers, and similarly cooling of the eye by cooling the body may also have deleterious effects. The heart responds to hypothermia with arrhythmias, and the blood clotting mechanisms may be severely impaired resulting in hemorrhage. Moreover, cooling the body only results in a few degrees of cooling of the CNS. In the case of the eye, attempts have been made to cool the vitreous of the eye during retinal and vitreous surgery by surgically entering the eye and cooling it from within. A recent animal study on viability of CNS tissue of the eye after hypothermia demonstrated similar preservation of function.
With the new technologies now available, it is time for a new approach to controlling the temperature of the CNS and the eye and orbit by doing local cooling from outside surface of the eye without entering the eye surgically. By administering medications to the eye/orbit directly in a continuous fashion coupled with hypothermia, there may be a new approach to treating eye disease.